1. Field of the Invention
This invention relates to a digital signal recording and/or reproducing apparatus, for example, to a digital signal recording and/or reproducing apparatus in which video signals, voice signals, data etc. are recorded as digital signals in a so-called PCM audio area of a magnetic tape employed in, for example, a so-called 8 mm video tape recorder, and in which recorded video signals, voce signals, data etc. are reproduced.
2. Prior Art
Among the apparatus for recording video signals, voice signals, computer data etc. on a recording medium, and reproducing the recorded video signals, voice signals, computer data etc., there are known a tape recorder for recording and/or reproducing mainly voice data, a video tape recorder for recording and/or reproducing mainly video data and a disc apparatus for recording and/or reproducing mainly computer data.
Specifically, in a 8 mm video tape recorder for recording and/or reproducing mainly video signals, referred to hereinafter as an 8 mm VTR, a magnetic tape 80 is wrapped around a so-called rotary head drum at an angle of 211.degree., and scanned helically by a pair of heads, referred to hereinafter as rotary heads, at an angular interval of 180.degree., for forming inclined tracks 81 on the magnetic tape 80, as shown in FIG. 13. In a video area 82 of each track 81, corresponding to rotation through 180.degree. of a rotary head drum, frequency modulated luminance signals, carrier color signals converted to low frequency signals and frequency modulated audio signals are recorded in accordance with frequency multiplexing together with tracking signals for tracking servo, such as pilot signals for so-called ATF (automatic track finding) control. In the remaining area of each track 81, corresponding to rotation through 30.degree. of the rotary head drum, that is a PCM audio area 83, non-linear quantized 8 bit/sample PCM audio signals are recorded after processing with so-called cross-interleaving encoding for error correction and appendage of synchronization signals, parity data and IDs. Along both sides of the magnetic tape 80, a cue track 84 and an audio track 85 are formed by scanning by stationary heads. Cue signals for locating or finding the addresses of the contents of recorded images are recorded in the cue track 84, while audio signals for after-recording, for example, are recorded in the audio track 85.
The format of the PCM audio area 83 is explained briefly.
With the NTSC system, there are recorded, in each track (corresponding to one field) of the PCM audio area, data of 1050 (=525/2.times.2 samples.times.2 channels: L0 to L524, R0 to R524) 8-bit words and 6 IDs, each consisting of 8 bits. Specifically, as shown in FIG. 14, each track of the PCM audio area is constituted by 132 (=(1050+6)/8) CRC (cyclic redundancy check) blocks. Turning to the format of each CRC block, 3-bit synchronization signals, 8-bit block address 8-bit Q-parity, 4-word data or ID, 8-bit Q-parity, 4-word data and 16-bit CRC code are arrayed in this order With the PAL system, the above figures are 1250 (=625/2.times.2 samples.times.2 channels : L0 to L624, R0 to R624) words/track and 157 (=(1250+6)/8)CRC block/track.
On the other hand, a video tape recorder having an increased frequency band for the video region, referred to hereinafter as Hi-8 mm VTR, has been marketed for improving the picture quality beyond the above mentioned 8 mm VTR, while researches are currently conducted for recording linearly quantized 16 bit/sample (or L mode) PCM audio signals or non-linearly quantized 12 bit/sample (or N mode) PCM audio signals in the PCM audio area for improving the sound quality.
The format of the PCM audio area, presently researched, is explained briefly.
On a magnetic track used in a Hi-8 mm VTR, inclined tracks are formed by helical scanning by the rotary head, similarly to the magnetic tape used for the above mentioned 8 mm VTR. In each track 91, corresponding to one field, there are recorded, from the leading end of the track, a margin area 94, a preamble area 95, a PCM audio area 93, a postamble area 96, a guard area 97 and a video area 92 for recording video signals, as shown in FIG. 15. The lengths of the margin area 94 and the preamble area 95, summed together, the lengths of the PCM audio area 93, postamble area 96 and the card area 97, summed together and the length of the video area 92, correspond to rotation through 5.degree., 36.degree. and 180.degree. of the rotary head drum, respectively.
Turning to a field format of the PCM audio area 93, for example, the NTSC system L mode, each track of the PCM audio area is constituted by 110 blocks, as shown in FIG. 16. In each block, a 4-symbol or byte header, 36-symbol data or Q-parity and 4-symbol P-parity are arrayed as shown. Specifically, the format of the 36-symbol data is such that, as shown in FIG. 17, 3240 (=36 bytes.times.90 blocks: L.sub.0U to L.sub.809U, L.sub.0L to L.sub.809L, R.sub.0U to R.sub.809U, R.sub.0L to L.sub.809L) byte data and 1160 (=4 bytes.times.110 blocks+36 bytes.times.20 blocks) byte parity are arrayed in each track.
The header format is such that, as shown in FIG. 18, synchronization signals, block address (BA), ID and the parity, each consisting of 8 bits, are arrayed. Meanwhile, with the PAL system, each track is composed of 132 blocks. Although the number of blocks in the N-mode is the same as that of the L-mode, the capacity of data recorded in each block is 27 symbols.
Meanwhile, although PCM audio signals are customarily recorded in the PCM audio area 82 of the 8 mm VTR or in the PCM audio area 92 of the Hi-8 mm VTR, it may be contemplated to use the 8 mm VTR or Hi-8 mm VTR not simply as an apparatus for recording and/or reproducing video signals, but as an apparatus for recording and/or reproducing various data, such as recording and/or reproducing video signals of a still picture or computer data as digital signals for enhancing the function or the usage of the apparatus.
However, in such case, the problem of interchangeability is raised to cause considerable inconveniences to users. For example, if a still picture is recorded using an 8 mm VTR having an additional function of recording video signals of a still picture as digital video signals in the PCM audio area and a magnetic tape on which the video signals of the still picture are recorded is to be reproduced by a conventional 8 mm VTR, the video signals of the still picture cannot be reproduced because the conventional 8 mm VTR is not provided with the function of reproducing the video signals of the still picture. Besides, the user is not apprised of the reason the digital signals recorded in the PCM audio area cannot be reproduced. On the other hand, computer data etc. recorded by a unique additional function developed by a producer cannot be reproduced by an 8 mm VTR produced by some other producer.
With recent enhancement of information, the kinds of the handled data, such as video signals, voice signals or computer data, are diversified. The kinds of data recorded and/or reproduced by digital signal recording and/or reproducing apparatus, such as 8 mm VTRs or Hi-8 mm VTRs, tend to be diversified, such that interchangeability cannot be maintained of data recorded by a function enhanced in future or a unique function developed by a producer.